Studies of the Phycomycetes of Iowa

Numerous papers and valuable collections of the Fungus Flora of the state have been contributed by earlier botanists. Due to the effort of such men as Halsted, Bessey, Arthur, Hitchcock, Holway and Pammel, a collection of over 200,000 specimens of the fungi of the state is assembled in the herbarium of Iowa State College and other prominent herbaria in America. These collections are listed and described in various papers which are scattered in numerous publications over a period of a half century. It is obvious, then, that in order that such material be of value to students of mycology, it would seem desirable to collect it into some tangible form, by reexamining the specimens in the herbarium of Iowa State College, revising the nomenclature to conform to the more recent researches; and collecting and summarizing the literature bearing on the fungus flora of the state

A Statistical Model of Magnetic Islands in a Large Current Layer

We develop a statistical model describing the dynamics of magnetic islands in very large current layers that develop in space plasma. Two parameters characterize the island distribution: the flux contained in the island and the area it encloses. We derive an integro-differential evolution equation for this distribution function, based on rules that govern the small-scale generation of secondary islands, the rates of island growth, and island merging. Our numerical solutions of this equation produce island distributions relevant to the magnetosphere and corona. We also derive and analytically solve a differential equation for large islands that explicitly shows the role merging plays in island growth.Comment: 4 pages, 3 figure

Cosmic ray cutoff prediction using magnetic field from global magnetosphere MHD simulations

International audienceRelativistic particles entering the Earth's magnetosphere, i.e. cosmic rays and solar energetic particles, are of prime space weather interest because they can affect satellite operations, communications, and the safety of astronauts and airline crews and passengers. In order to mitigate the hazards that originate from such particles one needs to predict the cutoff latitudes of such particles as a function of their energies and the state of the magnetosphere. We present results from a new particle tracing code that is used to determine the cutoff latitudes of 8-15Men-1 alpha particles during the 23/24 April, 1998 geomagnetic storm and the preceding quiet time. The calculations are based on four different geomagnetic field models and compared with SAMPEX observations of alpha particles in the same energy range. The geomagnetic field models under consideration are: (i) the International Geomagnetic Reference Field (IGRF) model, (ii) the Tsyganenko "89" model (T89c), (iii) the Tsyganenko "96" model (T96), and (iv) a global magnetohydrodynamic (MHD) model of Earth's magnetosphere. Examining 11 SAMPEX cutoff latitude observations we find that the differences between the observed and the predicted cutoff latitudes are 2.3° ± 2.0° (mean) and 7.9° (maximum difference) for the IGRF model; 3.9° ± 2.4° (mean) and 6.9° (maximum difference) for the T89c model; 4.0° ± 1.4° (mean) and 5.5° (maximum difference) for the T96 model; and 2.5° ± 1.7° (mean) and 7.0° (maximum difference) for the MHD model. All models generally predict cutoff latitudes equatorward of the SAMPEX observations. The MHD model results also show steeper cutoff energy gradients with latitude compared to the empirical models and more structure in the cutoff energy versus latitude function, presumably due to the presence of boundary layers in the MHD model

Search for an onset mechanism that operates for both CMEs and substorms

Substorms and coronal mass ejections have been cited as the most accessible examples of the explosive energy conversion phenomenon that seems to characterize one of the behavior modes of cosmic plasmas. This paper addresses the question of whether these two examples – substorms and CMEs – support or otherwise the idea that explosive energy conversion is the result of a single process operating in different places and under different conditions. As a candidate mechanism that might be common to both substorms and CMEs we use the Forbes catastrophe model for CMEs because before testing it appears to have the potential, suitably modified, to operate also for substorms. The essence of the FCM is a sudden onset of an imbalance of the forces acting on an incipient CME. The imbalance of forces causes the CME to start to rise. Beneath the rising CME conditions develop that favor the onset of magnetic reconnection which then releases the CME and assists its expulsion. Thus the signature of the FCM is a temporally ordered sequence in which there is first the appearance of force imbalance which leads to upward (or outward) motion of the CME which leads to magnetic reconnection under it which expedites rapid expulsion. We look for the FCM signature in the output of two global magnetospheric MHD simulations that produce substorm-like events. We find the ordered sequence of events as stated but with a significant difference: there is no plasmoid prior to the onset of rapid reconnection, that is, there is no counterpart to the incipient CME on which an imbalance of forces acts to initiate the action in the FCM. If this result – that rapid tailward motion precedes the rapid reconnection of substorm expansion – is ultimately verified by other studies, it suggests that a description of the cause of substorm expansion should identify the cause of the preceding rapid tailward motion, since this leads necessarily to rapid reconnection, whatever the reconnection mechanism turns out to be. Clearly then, it is important to identify the cause of the preceding tailward motion

Grain Elevators of South Dakota and Associated Farm Supply Businesses: Some Factors Affecting Their Growth and Future Prospects

The purpose of this study is to explore some of the characteristics of the South Dakota grain elevator and farm supply industry and to identify factors affecting the growth or survival of an elevator. It is possible by utilizing known economies of volume through their marketing systems, South Dakota producers could realize a savings of at least $19 million annually